The effects of grid angle on a modified Nordmøre-grid in the Nordic shrimp fishery

Published source details Grimaldo E. (2006) The effects of grid angle on a modified Nordmøre-grid in the Nordic shrimp fishery. Fisheries Research, 77, 53-59.
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This study is summarised as evidence for the following.

	Action	Category
	Use a different design or configuration of size-sorting escape grid/system in trawl fishing gear (bottom and mid-water) Action Link

Use a different design or configuration of size-sorting escape grid/system in trawl fishing gear (bottom and mid-water)

A replicated, controlled study in 2004 of an area of seabed in the Greenland Sea, Norway (Grimaldo 2006) found that changing the configuration (lowering the angle of installation) of a size-sorting escape grid in a shrimp trawl net reduced the capture of unwanted small fish, and improved the size-selectivity of haddock Melanogramus aeglefinus and Greenland halibut Reinhardtius hippoglossoides, but not cod Gadus morhua, compared to higher grid angles. Lowering the grid installation angle to 33° from an initial 36° increased the average escapement rate of unwanted fish (lower: 82%, initial: 67%), and a higher angle (39°) allowed an average escape of 73% of fish (data not statistically tested). The average length at which fish had a 50% chance of escape was greater with the lowered grid angle compared to the highest for haddock (lowest: 18.5 highest: 15.0 cm) and halibut (lowest: 22.6 highest: 20.9 cm), but similar between angles for cod (lowest: 17.3 cm, highest: 17.1). In addition, catches of the target species northern shrimp Pandalus borealis were reduced by 8% at the lowest grid angle, and by 4–6% at the intermediate and highest angles. Fishing trials took place in the Ice Fjord and Minke Bank (240–415 m depth), off Svalbard, from a research trawler in November–December 2004. Data were collected from 25 trawl deployments using a modified Nordmøre grid with tear-drop shaped bars instead of circular (‘Cosmos’ grid, 19 mm bar spacing), installed at three different angles: lowered (33.5°, 16 hauls), intermediate (36.8°, 5 hauls) and increased (38.1°, 5 hauls). A cover installed over the grid collected the escaping catch. See original paper for gear specifications.

(Summarised by: Chris Barrett)